Exam 1 - Lecture 3 Flashcards
Two components that determine cardiac output:
health of heart and health of system
increase of resistance to venous return will cause
less venous return and less cardiac output
e.g. Right atrial pressure 0mmHg has 5L/min of venous return at Psf of 7, but if RA pressure is +4 its 2.5L/min
If right atrial pressure increases, what needs to increase in order to raise venous return instead of lowering it?
Higher Psf. If it stays the same, then the delta P falls lower than 7 and it would decrease venous return.
Why is making the right atrial pressure negative not as effective as raising the right atrial pressure + also increasing Psf?
if its negative it can only go up to 6L/min bc the veins would collapse from the negative pressure.
If body needs to enhance CO for a marathon, it chooses to
Change the Psf!!!!
by tightening arteries to improve blood flow to muscles,
mesenteric arteries clamp down to shut down digestion
Increase BP
Increase venous constriction to raise Psf the most to improve blood returning to heart
Primary obstacle to blood returning to heart would be
Chest full of air can compress the vena cavae and return in less venous return, such as during positive pressure ventilation. Counter this by tightening up veins with phenylephrine or more air per breath.
What medication can tighten up veins to produce more venous return to heart?
Phenylepherine
Where does majority effect of phenylephrine work?
Tightens up the veins more than arteries, and only has to tighten up them a little bit
A hypoeffective heart will move the cardiac output curve to the
right
A hypereffective heart will move the cardiac output curve to the
left
IF someone has a heart problem, what happens to their CVP, and why?
increased and its because the heart cant pump it all out
If the heart is weakening, the catecholamines step up. but if its a long term issue, its scaled back and replaced by
volume retention and blood expansion at the kidneys. Norepi and epi increase water retention as well.
What is the max cardiac output if we maxed venous return but didnt do anything to the heart?
13L/min
When the body wants to increase CO, the main thing the body adjusts is
venous return
Output of the heart is geared by the
metabolic rate
Conditions that increase metabolic rate/cardiac output (from highest increase of CO to lowest increase)
Beriberi, AV shunts, hyperthyroidism, Anemia, pulm disease, pagets disease
Conditions that decrease metabolic rate
Removal of arms and legs, hypothyroidism (lowest metabolic demand).
When cardiac output is reduced due to less metabolic demand, what happens to peripheral resistance?
increased to allow less blood flow to tissues.
When cardiac output is increased due to more metabolic demand, what happens to peripheral resistance?
Decreased to allow more blood flow to tissues.
Beriberi
Vit B1 deficiency, makes cells much less efficient and need to use more energy now.
not common in US, usually only third world countries
Why does vascular resistance reduce with AV shunts?
its one more route for the blood to take, reducing resistance
Cardiac output is tightly linked to
oxygen consumption
Dinitrophenol
old weight loss drug that would drive up metabolic rate
need nervous system to cooperate in order to boost cardiac output on this chart (????)
How does dinitrophenol help with blood pressure?
keeps blood pressure from crashing.
arteries dilate and veins will constrict to produce more venous return and cardiac output
what drugs should we not take
gas station drugs
Cardiac index
L/min/M2
What is a normal body surface area
1.7M2
What is a normal Cardiac index for a healthy 20 year old 70kg patienrt
3L/min/M2
what age does our cardiac index max out?
10 years old
Whats a normal max cardiac index
4-5L/min/m2
cardiac index of a reasonably healthy 70 year old man
2.4L/min/m2
Why does our cardiac index lessen as we age?
less energy expenditure
which side of the heart has a steeper cardiac curve?
right ventricle..
think right atrial pressure is 0 and left atrial pressure is 2
CVP depends on where you measure.. right outside right atrium is ____ and then further from the heart the pressure gets _____
CLOSE to 0mmHg; higher due to DISTANCE
Mean circulatory filling pressure is same as
Psf
With an AV fistula, the filling pressure will be _____ and the cardiac output will be _______. Why?
normal;high; resistance to venous return is reduced
Reducing resistance to half will increase or decrease venous return?
Increase
During hemorrhagic shock, how does heart adjust?
increases right atrial pressure
normal intrapleural pressure is
-4mmHg
When right atrial pressure increases to +4, how does interpleural pressure change?
Becomes much higher, around +2mmHg
-4mmHg is equal to how much cmH2O
-5
When you take a breath, it sucks air into lungs but also
sucks blood into heart, therefore there is higher cardiac output
During exhalation, how does this adjust cardiac output?
decrease because there is more pressure in the intrapleural space
If there is increased intrathoracic pressure, there will be _____ cardiac output. Over time, the body will compensate by ____
reduced; increasing venous return by constricting the venous system
If there is a hypoeffective heart with reduced intrapleural pressure (more negative) then the hypoeffective heart will have a _____ shift with a _____ plateau
Left cardiac output curve; lower
A hypereffective heart with an increased intrapleural pressure will have what output shift and what plateau
Right shift; high plateau
How do arterial specific vasodilators cause increased venous return? Does it alter Psf?
Relax the arterioles to relax the “chokepoint” which will increase the pressure downstream into the venules, which will push the blood faster to the right heart.
This does NOT change the Psf
SVR is mainly governed where
arterioles
Specific example of arterial specific vasodilator?
ACE-I
Example of venous specific vasodilator is
nitroglycerin
Do venous specific vasodilators change Psf?
yes, it will reduce it
How does venous specific vasodilators change delta p?
lowers
whats the main purpose/effect of nitroglycerin?
reducing preload and the stress on the heart so it needs less oxygen
mixed vasodilators have what result on cardiac output?
dilates both vessels but since venous changes outweigh arterial, it slightly lowers venous return and Psf and therefore cardiac output
If we reduce volume or increase venous compliance, the cardiac output will
decrease
If we increase volume or decrease venous compliance, the cardiac output will
increase
Decreased SVR will result in
increased CO
Increased SVR will result in
decreased CO
If the heart is damaged, then how will body adjust
Venous compliance reduces (veins tighten up), increased volume retention, and increased SVR
